<template>
  <div class="pagination">
    <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{active:pageNo==1}">1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

    <!-- 中间部分 -->
    <button v-for="(page,index) in startNumAndEndNum.end" :key="index"
      v-if="page>=startNumAndEndNum.start" @click="$emit('getPageNo',page)" :class="{active:pageNo==page}">{{page}}</button>

    <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)"
      :class="{active:pageNo==totalPage}">{{totalPage}}</button>
    <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>

    <button style="margin-left: 30px">共 {{total}} 条</button>
    <!-- 测试数据 <h1>{{startNumAndEndNum}}---当前的页码{{pageNo}}</h1> -->
  </div>
</template>

<script>
export default {
  name: "Pagination",
  props:['pageNo','pageSize','total','continues'],
  computed: {
    //总共多少页
    totalPage() {
      //向上取整Math.ceil 
      return Math.ceil(this.total/this.pageSize)
    },
    //pageNo:当前第几页 pageSize:代表每一也展示多少条数据 total:代表整个分页一共要展示多少条数据 continues:代表分页连续页码个数
    //计算出连续的页码的起始数字与结束数字[连续页码的数字:至少是5]
    startNumAndEndNum(){
      //解构出来,不解构是作为实例身上的属性,不解构没法用
      const {continues,pageNo,totalPage} = this 
      //先定义两个变量存储起始数字与结束数字
      let start = 0,end = 0
      //连续页码数字5[就是至少5页],如果出现不正常的现象[就是不够5页]
      //不正常现象[总页数没有连续页码多]
      if(continues > totalPage){
        start = 1;
        end = totalPage;
      }else{
        //正常现象[连续页码5,但是你的总页数一定是大于5的]
        //起始数字
        start = pageNo - parseInt(continues / 2) //parseInt向下取整,这里代码主要是找规律,不能写死了
        //结束数字
        end = pageNo + parseInt(continues / 2)
        //把出现不正常的现象纠正[start数字出现0|负数]
        if(start < 1){
          start = 1;
          end = continues;
        }
        //把出现不正常的现象纠正[当前页就是如果和总页数相等,就会导致end大于总页数的问题]
        if(end > totalPage) {
          end = totalPage
          start = totalPage - continues + 1
        }
        return {start,end}//同时返回两个数据,只能以对象的形式返回
      }
    }
  }
};
</script>

<style lang="less" scoped>
.pagination {
  text-align:center;
  button {
    margin: 0 5px;
    // background-color: #9f9ffa;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active {
  background: skyblue;
}
</style>
